1. Field of the Invention
The present invention relates generally to the completion of oil and gas wells through fracturing operations, and more particularly, but not by way of limitation, to a jetting apparatus for cutting fan-shaped slots in a plane substantially perpendicular to a longitudinal axis of the well. The apparatus is will adapted for use on horizontal wells, but is not intended to be so limited.
2. Description of the Prior Art
Several different techniques are currently used for the completion of horizontal wells.
A first, very common manner of completing a horizontal well is to case and cement the vertical portion of the well and to leave the horizontal portion of the well which runs through the producing formation as an open hole, i.e., that is without any casing in place therein. Hydrocarbon fluids in the formation are produced into the open hole and then through the casing in the vertical portion of the well.
A second technique which is commonly used for the completion of horizontal wells is to place a length of slotted casing in the horizontal portion of the well. The purpose of the slotted casing is to prevent the open hole from collapsing. A gravel pack may be placed around the slotted casing. The slotted casing may run for extended lengths through the formation, for example as long as one mile.
A third technique which is sometimes used to complete horizontal wells is to cement casing in both the vertical and horizontal portions of the well and then to provide communication between the horizontal portion of the casing and the producing formation by means of perforations or casing valves. The formation may also be fractured by creating fractures initiating at the location of the perforations or the casing valves.
In this third technique, the formation of perforations is often done through use of explosive charges which are carried by a perforating gun. The explosive charges create holes which penetrate the side wall of the casing and penetrate the cement surrounding the casing. Typically, the holes will be in a pattern extending over a substantial length of the casing.
When the communication between the casing and the producing formation is provided by casing valves, those valves may be like those seen in U.S. Pat. No. 4,949,788 to Szarka et al., U.S. Pat. No. 4,979,561 to Szarka, U.S. Pat. No. 4,991,653 to Schwegman, U.S. Pat. No. 5,029,644 to Szarka et al., and U.S. Pat. No. 4,991,654 to Brandell et al., all assigned to the assignee of the present invention. Such casing valves also provide a large number of radial bore type openings communicating the casing bore with the surrounding formation.
When utilizing either perforated casing or casing valves like those just described, the fracturing fluid enters the formation through a large multitude of small radial bores at a variety of longitudinal positions along the casing and there is no accurate control over where the fracture will initiate and in what direction the fracture will initiate.
In the context of substantially deviated or horizontal wells, the cementing of casing into the horizontal portion of the well followed by subsequent fracture treatments has not been as successful as desired when using existing techniques, especially when multiple zone fracturing is involved.
The present invention solves these problems by providing a jetting apparatus which cuts the slots in the formation in a plane substantially perpendicular to the longitudinal axis of the well casing. In a preferred embodiment, a plurality of such slots are cut substantially simultaneously, and the apparatus insures that the slots are coplanar. This allows initiation of the fracture such that the fracture moves outwardly away from the wellbore so that the direction of the fracture will not be controlled by the local stresses immediately surrounding the casing and wellbore which might otherwise cause the fracture to follow the wellbore.